Palladium–S‐propyl‐2‐aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)

A moisture‐ and air‐stable heterogenized palladium catalyst was synthesized by coordination of palladium with S‐propyl‐2‐aminothiobenzamide supported on Fe₃O₄ magnetic nanoparticles. The prepared nanocatalyst was characterized using Fourier transform infrared, energy‐dispersive X‐ray and inductively coupled plasma atomic emission spectroscopies, X‐ray diffraction, vibrating sample magnetometry, transmission and scanning electron microscopies, dynamic laser scattering and thermogravimetric analysis. This catalyst could be dispersed homogeneously in water or poly(ethylene glycol) and further applied as an excellent nano‐organometal catalyst for Suzuki and Heck reactions. The catalyst was easily separated with the assistance of an external magnet from the reaction mixture and reused for several consecutive runs without significant loss of its catalytic efficiency or palladium leaching. The leaching of catalyst was examined using hot filtration and inductively coupled plasma atomic emission spectroscopy. Also, the effects of various reaction parameters on the Suzuki and Heck reactions are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Fe3O4@SiO2@l‐arginine@Pd(0): a new magnetically retrievable heterogeneous nanocatalyst with high efficiency for C–C bond formation

The surface of Fe₃O₄@SiO₂ nanoparticles was modified using l ‐arginine as a green and available amino acid to trap palladium nanoparticles through a strong interaction between the metal nanoparticles and functional groups of the amino acid. The proposed green synthetic method takes advantage of nontoxic reagents through a simple procedure. Characterization of Fe₃O₄@SiO₂@l ‐arginine@Pd(0) was done using Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, vibrating sample magnetometry and inductively coupled plasma analysis. The catalytic activity of Fe₃O₄@SiO₂@l ‐arginine@Pd(0) as a new nanocatalyst was investigated in C – C coupling reactions. Waste‐free, use of green medium, efficient synthesis leading to high yield of products, eco‐friendly and economic catalyst, excellent reusability of the nanocatalyst and short reaction time are the main advantages of the method presented. Copyright © 2016 John Wiley & Sons, Ltd.     

Logic for abstract hoop twist-structures

In this paper, we introduce and study a logic that corresponds to abstract hoop twist-structures and present some results on this logic. We prove the local deductive theorem for this logic and show that this logic is algebraizable with respect to the quasi-variety of abstract hoop twist-structures.     

Immobilization of a vanadium complex onto functionalized nanoporous MCM‐41 and its application as a catalyst for the solvent‐free chemoselective oxidation of sulfide to sulfoxide

A complex moiety containing VO(IV) was anchored covalently into organic‐modified Si‐MCM‐41 to prepare a new catalyst. The prepared materials were characterized using various techniques. Several types of aromatic and aliphatic sulfides were successfully oxidized to the corresponding sulfoxides in good to excellent yields using H₂O₂ in the presence of a catalytic amount of the catalyst under solvent‐free conditions. The results showed that the OH groups of the various compounds such as 2,2‐(phenylthio)ethanol and 2‐(methylthio)ethanol remained intact under similar conditions. Meanwhile the catalyst was stable in the reaction system, and could be reused at least four times without significant loss of its activity and chemoselectivity. Copyright © 2016 John Wiley & Sons, Ltd.     

Analytical elasto-creep model of interfacial thermal stresses and strains in trilayer assemblies

A two-dimensional model has been developed for thermal stresses, elastic strains, creep strains, and creep energy density at the interfaces of short and long trilayer assemblies under both plane stress and plane strain conditions. Both linear (viscous) and non-linear creep constitutive behavior under static and cyclic thermal loading can be modeled for all layers. Interfacial stresses and strains are approximated using a combination of exact elasticity solutions and elementary strength of materials theories. Partial differential equations are linearized through a simple finite difference discretization procedure. The approach is mathematically straightforward and can be extended to include plastic behavior and problems involving external loads and a variety of geometries. The model can provide input data for thermal fatigue life prediction in solder or adhesive joints. For a typical solder joint, it is demonstrated that the predicted cyclic stress–strain hysteresis shows shakedown and a rapid stabilization of the creep energy dissipation per cycle in agreement with the predictions of finite element analysis.     

Oxidative Diels-Alder reaction of 2, 5-dihydroxybenzoic acid with 1, 3-cyclopentadiene

The electrochemical oxidation of 2,5-dihydroxybenzoic acid (1) has been studied in the presence of 1,3-cyclopentadiene (2) as a diene in water/ethanol (40/60, v/v) mixture using cyclic voltammetry and controlled-potential coulometry. A plausible mechanism for the oxidation of 1 in the presence of 2 is presented. Compound 1 was converted into bis-adduct 5 via electrooxidation, Diels-Alder reaction of 2 to anodically generated 3,6-dioxocyclohexa-1,4-dienecarboxylic acid (1ox), decarboxylation reaction, electrooxidation and Diels-Alder reaction. The electrochemical synthesis of 5 was performed in a onepot reaction, without toxic reagents, at a carbon electrode in a simple cell using an environmentally friendly method.     

Zinc–aluminum layered double hydroxide as a nano-sorbent for removal of Reactive Yellow 84 dye from textile wastewater effluents

In this research, the zinc–aluminum layered double hydroxide (Zn–Al LDH) was synthesized and structurally and morphologically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy and N₂ adsorption–desorption techniques. The obtained nano-structured inorganic material was employed as an innovative nano-sorbent for separation of Reactive Yellow 84 (RY84) dye from aqueous solutions, which can be spectrophotometrically monitored at λ = 359 nm. The effect of several parameters such as type of interlayer anion in Zn–Al LDH structure, pH, sample flow rate, elution conditions, amount of nano-sorbent, sample volume and co-existing ions on the retention efficiency was investigated and optimized. The results showed that trace amounts of the RY84 could be retained using a column packed with 300 mg of the Zn–Al(NO₃ ^?) LDH at pH 8 and stripped by 2.5 mL of 3.0 mol L^?1 NaOH. Under the optimum experimental conditions, the limit of detection and the relative standard deviation were 0.04 μg mL^?1 and 1.8 %, respectively. The calibration graph using the presented solid phase extraction system was linear in the range of 0.15–1.5 μg mL^?1 with a correlation coefficient of 0.9982. The method was successfully applied to removal of RY84 from several textile wastewater effluents.     

Expeditious green synthesis of 3,4-disubstituted isoxazole-5(4<Emphasis Type="Italic">H</Emphasis>)-ones catalyzed by nano-MgO

In this work, it was found that magnesium oxide nanoparticles (nano-MgO) catalyzed one-pot three-component reaction of hydroxylamine hydrochloride with aryl aldehydes (or heteroaryl aldehydes) and β-oxoesters to synthesize some biologically active isoxazole-5(4H)-one-based heterocycles. The reactions were completed using 3 mol% catalyst loading in aqueous medium at room temperature. Nano-MgO was synthesized by precipitation and hydrothermal treatment of aqueous salt solution. The structure of the nano-MgO was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The presented environmentally friendly heterocyclization offers some interesting merits, including safety, high product yield, mild conditions, low cost, minimal waste, good atom efficiency, catalyst recoverable, energy efficiency, avoidance of hazardous organic solvents, and easy workup.     

Preconcentration and determination of naproxen in water samples by functionalized multi-walled carbon nanotubes hollow fiber solid phase microextraction—HPLC

A simple, sensitive and selective solid phase microextraction with hollow fiber-supported multi-walled carbon nanotube functionalization reinforced sol–gel combined HPLC method was proposed for the determination of naproxen in tap, well and river water samples. In this method, functionalized multi-walled carbon nanotubes (MWCNTs) were prepared and held in pores of hollow fiber with sol–gel technology by immersion of polypropylene hollow fiber segment into the sol of the functionalized MWCNTs/silica composite and ultrasonically treated at room temperature. Effect of main parameters such as volume of donor phase, pH, extraction time, desorption time, type of desorption solvent, sample ionic strength and stirring rate were studied. Under optimum conditions, linearity was observed in the range of 0.03–500 ng/mL, with correlation coefficients of 0.997. The relative standard deviation for three replicate determinations of 50 ng/mL of naproxen was 4.3%. Limit of detection and pre-concentration factor were 0.008 ng/mL and 198, respectively. In order to check the applicability of the proposed method, it was used to determine trace levels of naproxen in different water samples.     

On eigenvalues of Seidel matrices and Haemers’ conjecture

For a graph G, let S(G) be the Seidel matrix of G and \({\theta }_1(G),\ldots ,{\theta }_n(G)\) be the eigenvalues of S(G). The Seidel energy of G is defined as \(|{\theta }_1(G)|+\cdots +|{\theta }_n(G)|\). Willem Haemers conjectured that the Seidel energy of any graph with n vertices is at least \(2n-2\), the Seidel energy of the complete graph with n vertices. Motivated by this conjecture, we prove that for any \(\alpha \) with \(0<\alpha <2,|{\theta }_1(G)|^\alpha +\cdots +|{\theta }_n(G)|^\alpha \geqslant (n-1)^\alpha +n-1\) if and only if \(|\hbox {det}\,S(G)|\geqslant n-1\). This, in particular, implies the Haemers’ conjecture for all graphs G with \(|\hbox {det}\,S(G)|\geqslant n-1\). A computation on the fraction of graphs with \(|\hbox {det}\,S(G)|<n-1\) is reported. Motivated by that, we conjecture that almost all graphs G of order n satisfy \(|\hbox {det}\,S(G)|\geqslant n-1\). In connection with this conjecture, we note that almost all graphs of order n have a Seidel energy of order \(\Theta (n^{3/2})\). Finally, we prove that self-complementary graphs G of order \(n\equiv 1\pmod 4\) have \(\det S(G)=0\).